Bounce-free magnet actuator for injection valves

ABSTRACT

The invention relates to a magnet valve for actuating a fuel injector, having a magnet core and a magnet coil received in the core. A closing spring acts on the magnet armature in the closing direction. An outlet gap for an actuating fluid is formed between a face end of the stop sleeve, oriented toward the magnet armature, and the magnet armature itself. The outlet gap discharges into a hydraulic damping chamber, which is defined by a face end of the magnet armature and by a damping face of the non-magnetic material.

FIELD OF THE INVENTION

In fuel injection valves, actuators are used, such as piezoelectricactuators or magnet valves. Triggering the actuators initiates apressure relief of a control chamber, causing an injection valve toopen, so that fuel can be injected into the combustion chamber of aninternal combustion engine. However, magnet valves have the property oftending to bounce, and as a result the performance graph for thequantity, that is, the injection quantity, can vary so much relative tothe triggering time that it is only conditionally suitable forreproduction or for compensation functions.

BACKGROUND OF THE INVENTION

European Patent Disclosure EP 0 562 046 B1 discloses an actuation andvalve assembly with damping for an electronically controlled injectionunit. The actuation and valve assembly for a hydraulic unit has anelectrically excitable electromagnet assembly with a fixed stator and amovable armature. The armature includes a first and a second surface.The first and second surfaces of the armature define a first and secondhollow chamber, and the first surface of the armature is oriented towardthe stator. A valve is provided which is connected to the armature. Thevalve is capable of carrying a hydraulic actuating fluid from a sump tothe injection system. A damping fluid can be collected there relative toone of the hollow chambers of the electromagnet assembly and drainedaway from there again. By means of a region of a valve needle protrudinginto a central bore, the fluidic communication of the damping fluid canbe selectively opened and closed in proportion to the viscosity of thisfluid.

German Patent Disclosure DE 101 23 910.6 pertains to a fuel injectionsystem. This system is used in an internal combustion engine. Thecombustion chambers of the engine are supplied with fuel via fuelinjectors. The fuel injectors are acted upon in turn via a high-pressuresource; moreover, the fuel injection system includes a pressure boosterwhich has a movable pressure booster piston. This piston divides achamber that can be connected to the high-pressure source from ahigh-pressure chamber that communicates with the fuel injector. The highfuel pressure in the high-pressure chamber can be varied, by filling aback chamber of a pressure boosting device or by evacuating fuel fromthis back chamber of the fuel booster.

In magnet valves of the prior art, the stroke length is defined by stopsleeves, to name one example. In addition, in magnet valves that havetwo seats, the stroke of the magnet valve can be defined by the twoseats. In such magnet valves, bouncing can occur at the first, upperseat. The same is true for a valve that is open when without current andthat has only one seat. If stop sleeves are received in the magnet core,they surround a closing spring that acts on the magnet armature. Bymeans of a stop sleeve, the precise adjustment of a remanent air gapbetween the magnet core and the magnet armature, or its armature plate,can be accomplished. In fast opening of the magnet valve, which isdesired, the armature comes to strike one face end of the stop sleeve,which is called armature bouncing. The armature bouncing on the stopsleeve has effects on the quantity performance graph, or in other wordsthe injection quantity of fuel, relative to the triggering duration of amagnet coil of a magnet valve that actuates a fuel injector. In someapplications, the effects of armature bouncing on the quantityperformance graph are wanted, such as if a preinjection quantity plateauis desired for a phase of preinjection into the combustion chamber.However, in conjunction with regulating a preinjection quantity, as willbe needed for fuel injection systems expected in the future, a quantityperformance graph that has a preinjection quantity plateau is extremelyunfavorable.

SUMMARY OF THE INVENTION

With the embodiment proposed according to the invention, the armaturebouncing that affects the quantity performance graph of a fuel injectoris reduced considerably, by the creation of a surface area that buildsup a damping force. Although in previously employed embodiments only theend face of a stop sleeve and the end face of a magnet core wereavailable as a surface area that generates a damping force, with theembodiment proposed according to the invention a targeted increase inthe damping can be achieved.

The damping face, embodied on the side of the magnet core toward themagnet armature, is made of non-magnetic material, such as plastic.Plastic material has the advantage that it can easily be worked. Thismaterial can either be glued to the magnet core or cast on it. The easyworkability of the plastic material also offers the advantage that thedamping performance can be adjusted in a targeted way by the embodimentof an angle relative to the plane end face of the magnet armature. Inprinciple, all materials that have no or only slight effects on themagnetic circuit can be used to produce the damping face.

The damping face can extend on the face end of the magnet core towardthe magnet armature both parallel to this face end and at a dampingadjustment angle, relative to the end face of the magnet armature. Thedesired damping behavior can be established by the choice of the dampingadjustment angle. Besides a hydraulic damping chamber that opens outwardin the radial direction, this damping chamber can also narrowincreasingly outward, in terms of the radial direction, relative to theaxis of symmetry of the magnet coil and of the magnet armature. Anunwanted, premature outflow of the damping fluid (such as fuel) from thehydraulic damping chamber can be attained by the embodiment of a luglikeprotrusion on the outside radius of the hydraulic damping chamber. Uponfast opening of the magnet armature, the luglike protrusion acts as athrottling element, and upon an upward motion of the magnet armature, iteffects throttling of the flow of the actuating fluid, such as fuel orDiesel fuel, from the hydraulic damping chamber upon opening of themagnet armature. By means of the choice of a non-magnetic material, themagnetic properties of the magnet valve—in particular, the preservationof the remanent air gap—remain unimpaired.

DRAWING

The invention is described in further detail below in conjunction withthe drawing.

Shown are:

FIG. 1, a magnet valve whose stroke length is defined by a stop sleeve;

FIG. 2, a magnet valve embodied according to the invention, with amagnet core which has a surface area that generates a damping force;

FIG. 3, a magnet core with a stop sleeve located on the outside;

FIG. 4, pressure distributions in the hydraulic damping chamber, in thevariant embodiments of FIGS. 2 and 3;

FIG. 5, the comparison of damping forces that are established in thevariant embodiments of FIGS. 2 and 3; and

FIG. 6, a variant embodiment of a magnet core without a stop sleeve.

VARIANT EMBODIMENTS

FIG. 1 shows a magnet valve of the prior art, whose stroke length isdefined by a stop sleeve.

A magnet valve 1, which is used to actuate a fuel injector forself-igniting internal combustion engines, includes a magnet core 2. Amagnet coil 3 is let into the magnet core 2. The magnet core 2 includesa first end face 4 and a second end face 5 that points toward a magnetarmature 10. A bore 6 is embodied in the magnet core 2, and a stopsleeve 7 is let into the bore. A face end 8 is embodied on the lower endof the stop sleeve 7 and forms a stop for one face end 12 of an armatureplate 11 of the magnet armature 10. The stop sleeve 7 surrounds aclosing spring 9, which urges the face end 12 of the magnet armature 10in the closing direction. The face end 12 of the magnet armature 10 isembodied on its armature plate 11. In the variant embodiment of themagnet valve known from the prior art, the magnet armature 10 isembodied as a one-piece armature; that is, the armature plate 11 and thearmature bolt of the magnet armature 10 form a single component.Alternatively, the armature plate 11 of the magnet armature 10 may alsobe embodied displaceably on the armature bolt. In that case, or in otherwords with a magnet armature embodied in two parts, the armature plate11 is acted upon via a spring element which surrounds the armature bolt.

Reference numeral 13 indicates a remanent air gap, which defines thespacing between the second end face 5 of the magnet core 2 and the faceend 12 of the armature plate 11 of the magnet armature 10. In thevariant embodiment, shown in FIG. 1, of a magnet valve 1 with a stopsleeve 7, the magnet coil 3 is let in on the lower region of the magnetcore 2, establishing an annularly configured free space 14 between theunderside of the magnet coil and the second end face 5 of the magnetcore 2. The annularly configured free space 14 between the underside ofthe magnet coil 3 and the end face 12 of the armature plate 11 of themagnet armature 10 exceeds the remanent air gap 13; the spacing betweenthe magnet coil 3 and the top 12 of the armature plate 11 is identifiedby reference numeral 15.

In the variant embodiment of a magnet valve shown in FIG. 1, the strokeof the magnet valve 1 is defined via the stop sleeve 7; that is, theface end 8 of the stop sleeve 7 acts as a stop face for the face end 12of the armature plate 11 of the magnet armature 10, when the magnetvalve opens in response to an excitation of the magnet coil 3 and movesupward—in the direction of the stop sleeve 7. Via the relative positionof the stop sleeve 7 to the magnet core 2, the remaining remanent airgap 13 between the first end face 5 of the magnet core 2 and the faceend 12 of the armature plate 11 can be adjusted with extreme precision.On the other hand, upon the desired fast opening of the magnet valve1—the opening motion of the magnet armature 10 upon excitation of themagnet coil 3—the face end 12 of the magnet armature 10 strikes (bounceson) the face end 8 of the stop sleeve 7. This phenomenon, also calledarmature bouncing, has effects on the quantity performance graph, thatis, on the injected fuel quantity, plotted over the triggering durationof the magnet coil 3. In the variant embodiment of the magnet valveknown from the prior art and shown in FIG. 1, upon opening of the magnetvalve 1 a fluid—such as Diesel oil or some other type of fuel—isexpelled out of the narrow gap between the face end 8 of the stop sleeve7 and the face end 12, which upon opening of the magnet armature 10moves toward the face end 8 of the stop sleeve 7. This creates a forcethat damps the upward motion of the magnet armature 10. However, sincethe face end 8 of the stop sleeve 7 is very small, the damping forcegenerated at the face end 8 by the expelled fuel volume does not sufficeto prevent bouncing of the magnet armature 10, that is, of the face end12 of the armature plate 11, on the face end 8 of the stop sleeve 7. Theresult is an impact of the face end 12 of the armature plate 11 of themagnet armature 10 on the face end 8 of the stop sleeve 7 and recoiling.The armature bouncing of a magnet armature 10 has a major influence onthe flight time of the magnet armature from the onset of opening untilthe ensuing closure of the magnet valve. Because of the flight time ofthe magnet armature 10, influenced by the armature bouncing, from theonset of opening until the ensuing closure of the magnet armature 10,the fuel volume diverted from a control chamber of the fuel injector issubjected to fluctuations, which can lead to imprecisions in terms ofthe generation of a reciprocating motion—whether it is an opening or aclosing motion—of an injection valve member provided in the fuelinjector.

FIG. 2 shows a magnet valve embodied according to the invention, with amagnet core which has a surface area that generates a damping force.

In FIG. 2, a magnet core 2 is seen, shown in half section relative toits axis of symmetry. Analogously to the magnet core 2 as shown in FIG.1, the magnet core 2 shown in FIG. 2 has both a first end face 4 and asecond end face 5. The magnet coil 3 is let into the interior of themagnet core 2. Moreover, the bore 6 in which the stop sleeve 7 isreceived is embodied on the magnet core 2. The diameter of the bore 6 ofthe magnet core 2 is identical to an outside diameter 28 of the stopsleeve 7. The stop sleeve 7 in turn includes a closing spring 9, ofwhich only one winding is shown here in section, and which urges amagnet armature 10, shown only in fragmentary form in FIG. 2, in theclosing direction.

Of the magnet armature 10 shown in FIG. 1, FIG. 2 shows only thearmature plate 11, whose face end is identified by reference numeral 12.Upon opening of the magnet armature 10, an outlet gap 18 for fuel formsbetween the face end 8 of the stop sleeve 7 and the face end 12 of thearmature plate 11 of the magnet armature 10. According to the invention,the outlet gap 18, extending annularly between the face end 8 of thestop sleeve 7 and the face end 12 of the armature plate 11 of the magnetarmature 10, discharges into a radially extending hydraulic dampingchamber 31.

The hydraulic damping chamber 31 is defined toward the magnet core 2, onthe second end face 5 thereof, by a damping face 20, which begins at theoutside diameter 28 of the stop sleeve 7 and extends as far as thecircumference 27 of the magnet core 2. Moreover, the hydraulic dampingchamber 31 is defined by the face end 12 of the armature plate 11 of themagnet armature 10. The damping face 20 toward the magnet armaturecomprises a non-magnetic material 16, such as plastic material, so asnot to impair the magnetic properties of the magnet valve 1. Theattainable damping force can be adjusted by means of the geometry of thedamping face 20, which generates a damping force that counteracts theopening motions of the armature plate 11 of the magnet armature 10.

On the second end face 5 of the magnet core 2, which faces the face end12 of the armature plate 11 of the magnet armature 10, the damping face20 that defines the hydraulic damping chamber 31 can at a constantspacing 15; that is, fuel emerging parallel to the face end 12 of thearmature plate 11 and to the face end 8 of the stop sleeve 7 enters thehydraulic damping chamber 31. In this variant embodiment, the hydraulicdamping chamber 31 has a constant cross section extending in the radialdirection.

In a further variant embodiment of the hydraulic damping chamber 31, thedamping face 20 may be embodied at an angle 17 on the second end face 5of the magnet core 2. In this variant embodiment, the spacing betweenthe face end 12 of the armature plate 11 of the magnet armature 10 andthe damping face 20 on the second face end 5 of the magnet core 2increases continuously in the radial direction. As a result, it isattained that the fuel flowing into the hydraulic damping chamber 31from the outlet gap 18 generates a damping force, counteracting theopening motion of the armature plate 11 of the magnet armature 10, thatis greater than the damping force that can be generated by only the faceend 8 of the stop sleeve 7 (as shown in FIG. 1). By the choice of theangle 17, the surface area that generates the damping force can beincreased, and as a result, the damping force that counteracts theopening motion of the magnet armature 10 or of the armature plate 1 canalso be increased considerably.

A further variant embodiment of a hydraulic damping chamber 31 providesthat a luglike protrusion 32 be made on the damping face 20, on thesecond end face 5 of the magnet core 2. This luglike protrusion 32 onthe second end face 5 of the magnet core 2, when the armature plate 11of the magnet armature 10 moves upward in the opening direction, effectsthrottling of the fuel volume flowing out of the hydraulic dampingchamber 31, as a result of which the damping force acting on the magnetarmature 10, that is, on its armature plate 11, can be increased, sincethe throttle restriction between the end face 12 of the armature plate11 and the luglike protrusion 32 becomes smaller and smaller in thecourse of the opening motion of the magnet armature 10. Because of thereduction in size of the throttle restriction, that is, of the spacingbetween the face end 12 of the armature plate 11 and the luglikeprotrusion 32, the fuel volume entering the hydraulic damping chamber 31through the outlet gap 18 is capable of flowing out of this chamber onlyin delayed fashion, so that inside the hydraulic damping chamber 31, adamping volume that develops a damping action remains. The outletopening for the fuel volume flowing out of the damping chamber isidentified by reference numeral 35.

The damping face 20, which is made of a non-magnetic material 16, may beeither glued to the second end face 5 of the magnet core 2 or cast onthe second end face 5 of the magnet core 2. If the damping face 20 ismade of a non-magnetic material 16 such as plastic material, then bysuitable working of the damping face 20, such as grinding machining, theangle 17 that definitively affects the damping behavior can be adjustedin a targeted way.

The damping face 20 on the second end face 5 of the magnet core 2includes a first annular face portion 21, which extends from the outsideradius 28 of the stop sleeve 7 to the inside radius 25 of the magnetcoil 3 inside the magnet core 2. The damping face 20 furthermoreincludes a second annular face portion 22, which extends from the insideradius 25 of the magnet coil 3 to its outside radius 26, and a thirdannular face portion 23, which extends from the outside radius 26 of themagnet coil 3 inside the magnet core 2 to the outer circumference 27 ofthe magnet core 2. Inside the third annular face portion 23, theaforementioned luglike protrusion 32 that develops a throttling actioncan be embodied on the damping face 20 that defines the annularlyconfigured hydraulic damping chamber 31; with the face end 12 of thearmature plate 11, this protrusion defines an outlet opening 35, whoseopening cross section is dependent on the stroke length and the speed ofmotion of the magnet armature 10.

Inside the magnet core 2 of the magnet valve 1 as shown in FIG. 2, themagnet coil 3 is received in an annularly configured recess 24. On thesecond end face 5 of the magnet core 2, the recess 24 defines a firstedge 33 and a second edge 34. In the annular chamber defined by thefirst edge 33 and the second edge 34, the damping face can be glued inor cast in by positive engagement, so that the damping face is fixed inthe radial direction. In the case of the damping face 20 shown in FIG. 2and embodied at an angle 17 to the end face 12 of the armature plate 11,the first edge 33 creates a graduation 29 of the damping face 20relative to the second end face 5 of the magnet core 2. Both thegraduation and the fixation of the damping face 20 on the second endface 5 of the magnet core 2 by the first edge 33 and the second edge 34in the radial direction have the effect that the damping face 20 of themagnet core 2 is received in stationary fashion, and when the fuelvolume entering the hydraulic damping chamber 31 from the outlet gap 18shoots in, the damping face remains reliably in position and does notmigrate outward in the radial direction. The graduation 29 or 30 of thehydraulic damping face 20 that develops as shown in FIG. 2 relative tothe second end face 5 of the magnet core 2 is especially effective ifthe damping face 20 is made of a non-magnetic material 16, such asplastic material, that is cast on the second end face 5 of the magnetcore 2.

As can also be learned from FIG. 2, the luglike protrusion 32 of thedamping face 20 on the second end face 5 of the magnet core 2 ispreferably attached from above the outer edge of the armature plate 11of the magnet armature 10. As a result, upon the opening motion of thearmature plate 11 in the direction of the luglike protrusion 32, athrottle restriction is formed which decreases continuously in sizeduring the opening motion of the magnet armature 10 or armature plate11, so that the outflowing fluid 31, when the magnet armature 10 orarmature plate 11 is opening, is forced as a result to flow out througha constantly decreasing cross section in the radial direction. Becauseof the remaining fuel volume in the hydraulic damping chamber 31, thedamping force attainable with reference numeral 19 is markedly higherthan when there is an unhindered outflow of the fuel volume from thehydraulic damping chamber 31 in the radial direction. Because thedamping face 20 that creates the damping force 19 and defines thehydraulic damping chamber 31 is made of a non-magnetic material 16, themagnetic properties of the magnet valve 1 remain unchanged. The dampingface 20 is located in the remanent air gap 13 between the second endface 5 of the magnet core 2 and the face end 12 of the armature plate 11of the magnet armature 10 (see the view in FIG. 1). Because the dampingface 20 is embodied of a non-magnetic material 16 in the remanent airgap 13 of the magnet valve 1, the surface area that creates the dampingforce 19 can be designed such that a targeted amplification of thedamping force 19 is established. If a non-magnetic material 16 such asplastic is cast on the second end face 5 of the magnet core 2, then thebouncing behavior of the magnet armature 10 or armature plate 11 can beadjusted in a targeted way by adjusting the angle 17 by means of simplegrinding machining.

In FIG. 3, a magnet core with a stop sleeve located on the outside canbe seen. The magnet core 2 includes a first, upper end face and asecond, lower end face 5. A magnet coil 3 is received in the magnet core2, in the recess 24. The magnet core 2 as shown in FIG. 3 is surroundedby a stop sleeve 7 that surrounds the outer circumference 27 of themagnet core 2. The end face of the stop sleeve 7 is indicated byreference numeral 8. The magnet core 2, which is embodied essentiallyannularly, surrounds a closing spring 9, of which only one winding isshown in FIG. 3. The armature plate 11 of a magnet armature is locatedbelow the magnet core 2. The armature plate 11 has a face end 12. Anon-magnetic filler 16 is received on the second end face 5 of themagnet core 2, and its damping face 20 together with the face end 12 ofthe armature plate 11 defines the hydraulic damping chamber 31.

The non-magnetic filler 16 extends on the second end face 5 of themagnet core 2 over a first annular face portion 21, over a secondannular face portion 22 adjoining the first, and through a third annularface portion 23. The non-magnetic filler 16 has a first step 29 and asecond step 30 and can be cast or glued onto the second end face 5 ofthe magnet core 2. The steps 29 and 30 of the non-magnetic filler 16form a first edge 33 and a second edge 34, respectively, which engagethe recess 24 in the magnet core 2 and secure the non-magnetic filler 16radially relative to the magnet core 2 by positive engagement.

In the view in FIG. 3, the non-magnetic filler 16 is disposed on thesecond end face 5 of the magnet core 2 such that a damping adjustmentangle 17 is created which extends conversely to the damping adjustmentangle 17 shown in FIG. 2. The hydraulic damping chamber 31 thus narrows,viewed in the radial direction, toward the stop sleeve 7 that surroundsthe magnet core 2 in its outer circumference 27. The outside radius ofthe stop sleeve 7 as shown in FIG. 3 is identified—relative to the lineof symmetry—by reference numeral 28.2. The damping force 19, whichresults because of the inflow of fuel into the hydraulic damping chamber31 that becomes narrower outward, shown in the variant embodiment ofFIG. 3, is indicated by reference numeral 19. The spacing 15 identifiesthe gap height through which fuel flows into the hydraulic dampingchamber 15 from the inside of the hydraulic damping chamber 31.

FIG. 4 compares pressure distributions in the hydraulic damping chamberin the variant embodiments of FIG. 2 and FIG. 3.

In the variant embodiment shown in FIG. 2 of a hydraulic damping chamber31, which opens toward the outside in terms of the radial direction, afirst course of the pressure distribution 40 is established, which isdistinguished by a first maximum 41 located farther inward in the radialdirection of the hydraulic damping chamber 31. The maximum 41 is locatedapproximately inside the first annular face portion 21 as shown in FIG.2. By comparison, in the variant embodiment of FIG. 3, a second courseof the pressure distribution 42, which is characterized by a secondmaximum 43. The second maximum 43 of the variant embodiment of FIG. 3 islocated inside the third annular face portion 23; that is, it is locatedwhere the hydraulic damping chamber 31 is most severely narrowed.

FIG. 5 shows a comparison of the courses of the damping force that areestablished in the variant embodiments of FIGS. 2 and 3. The dampingforce 19 that is established in the hydraulic damping chamber 31 of thevariant embodiment in FIG. 2 is identified by reference numeral 44. Thecourse of the damping force established in the hydraulic damping chamber31 in FIG. 3 is identified by reference numeral 45. The level of thedamping force established in the hydraulic damping chamber 31represented by the first course 44 of the damping force is considerablybelow the level of the damping force 19 in the second course 45 of thedamping force that can be attained with the variant embodiment of FIG.3. It is true of both courses 44, 45 of the damping force that thedamping force decreases steadily with an increasing stroke, taking theremanent air gap into account, and reaches its minimum at the maximumstroke of the armature plate 11 in the direction of the magnet core 2.An estimate of the courses 44, 45 of the damping force can be made forsimple geometries using the lubrication gap theory.${\eta\frac{{\partial^{2}u}\quad{\partial p}}{{\partial y}\quad{\partial r}}},{{u\left( {y = 0} \right)} = 0},{{u\left( {y = h} \right)} = 0}$from which, the following is true:${U(y)} = {\frac{{\partial{py}^{2}} - {h \cdot y}}{{\partial r}\quad 2\eta}.}$

From the above equation, the volumetric flow in the pinch gap is foundby integration to be${\overset{.}{V}(r)} = {{\int_{o}^{h}{{u(y)} \cdot \quad{\mathbb{d}y}}} = {\frac{{B \cdot h^{3}}{\partial p}}{12\eta\quad{\partial r}}.}}$

The continuity equation leads to a differential equation for thepressure in the gap between the armature plate 11 and the magnet core 2,in accordance with the following equation:${\frac{\partial\overset{.}{V}}{\partial r} = {{- B} \cdot v}},{{p\left( r_{1} \right)} = 0},{{p\left( r_{o} \right)} = 0.}$

In this equation, v is the velocity [speed] of the magnet armature and pis the gap width: B=2π·r. For simple geometries, such as a conical gapas in FIGS. 2 and 3 or a level gap in FIG. 6, the differential equationcan be solved analytically.

FIG. 6 shows a variant embodiment of a magnet core that is embodiedwithout a stop sleeve.

It can be seen from FIG. 6 that the second end face 5 of the magnet core2 is embodied as essentially plane. The magnet coil 3 is let into therecess 24 of the magnet core 2. The magnet coil 3 does not, however,completely fill the recess 24 in the magnet core 2. A non-magneticfiller 16 is cast or glued into the openings in the recess 24 on thesecond end face 5 of the magnet core 2 and represents a damping face 20that extends in plane form relative to the face end 12 of the armatureplate 11. The non-magnetic filler 16 in the variant embodiment shown inFIG. 6 also has a first step 29 and a second step 30. Because of thegraduation of the non-magnetic filler 16, a first edge 33 and a secondedge 34 are created, with which the non-magnetic filler 16 is locked onthe underside of the recess 24 by positive engagement on the second endface 5 of the magnet core 2. In this variant embodiment, the hydraulicdamping chamber 31 has a cross section that extends outward constantlyin the radial direction relative to the line of symmetry shown.

Unlike the variant embodiment, shown in FIGS. 2 and 3, of a hydraulicdamping chamber 31 between the magnet core 2 and the armature plate 11,the hydraulic damping chamber 31 extends at a constant height throughthe annular face portions 21, 22 and 23. The hydraulic damping chamber31 is operative only whenever pure liquid is located in the hydraulicdamping chamber 31. If there is air or a mixture of air and liquidthere, such as foam, then the attainable hydraulic damping, and inparticular the first and second courses of the damping force 44 and 45shown in FIG. 5, are impaired severely.

With the variant embodiments described above, whether they are theembodiment of a damping face 20 extending parallel at a constant spacing15 between the second end face 5 and the face end 12 of the armatureplate 1, or a damping face 20 with an angle 17 or a damping face 20 witha luglike protrusion 32, the quantity performance graph of a fuelinjector can be improved considerably, and in particular, a quantityperformance graph free of plateaus can be brought about. If acharacteristic curve for a particular high-pressure level within afamily of characteristic curves has a preinjection plateau, and ifwithin this preinjection plateau the triggering duration is changed,then the quantity of fuel injected into the combustion chamber of theself-igniting internal combustion engine remains constant. Thecharacteristic curves, established by the embodiment proposed accordingto the invention, for fuel pressures within a family of characteristiccurves have a strongly monotonously increasing course, or in other wordswithout any preinjection plateau. This in turn means that when thetriggering duration is longer, more fuel will always be injected intothe combustion chamber of the engine. This is the fundamentalprerequisite for a zero-quantity calibration of a fuel injector. Aplateau-free quantity performance graph is especially helpful inzero-quantity calibration of the fuel injector while the vehicle is inoperation. Moreover, the embodiment proposed according to the inventionof a hydraulic damping chamber 31 between the second end face 5 of themagnet core 2 and the face end 12 of the armature plate 11 of the magnetarmature 10 makes it possible to reduce noise during operation of a fuelinjector.

List of Reference Numerals

-   1 Magnet valve-   2 Magnet core-   3 Magnet coil-   4 First end face-   5 Second end face-   6 Bore-   7 Stop sleeve-   8 Face end-   9 Closing spring-   10 Magnet armature-   11 Armature plate-   12 Face end of armature plate-   13 Remanent air gap-   14 Free space-   15 Spacing-   16 Non-magnetic filler-   17 Angle-   18 Outlet gap-   19 Damping force-   20 Damping face-   21 First annular face portion-   22 Second annular face portion-   23 Third annular face portion-   24 Recess, magnet core-   25 Inside radius, magnet coil-   26 Outside radius, magnet coil-   27 Outer circumference, magnet core-   28.1 First outside radius, stop sleeve-   28.2 Second outside radius, stop sleeve-   29 First graduation-   30 Second graduation-   31 Hydraulic damping chamber-   32 Luglike protrusion-   33 First edge-   34 Second edge-   35 Outlet opening between 32 and 12-   40 First course of pressure distribution-   41 First pressure maximum-   42 Second course of pressure distribution-   43 Second pressure maximum-   44 First damping force course-   45 Second damping force course

1-17. (canceled)
 18. In a magnet valve for actuating a fuel injector,having a magnet core (2), in which a magnet coil (3) is received thatsurrounds a closing spring (9), which acts on a magnet armature (10),and between a face end (8) oriented toward the magnet armature (10) andthe magnet armature (10), outlet openings (18, 35) are formed uponimpact of the magnet armature (10), the improvement comprising ahydraulic damping chamber (31) defined by one face end (12) of themagnet armature (10) and by a damping face (20) of non-magnetic material(16).
 19. The magnet valve of claim 18, wherein the hydraulic dampingchamber (31) extends in the radial direction.
 20. The magnet valve ofclaim 18, wherein the hydraulic damping chamber (31) is embodied as anannular chamber.
 21. The magnet valve of claim 19, wherein the dampingface (20) is embodied of non-magnetic material (16) on the second endface (5), oriented toward the magnet armature (10), of the magnet core(2).
 22. The magnet valve of claim 21, wherein the damping face (20)extends on the second face end (5) of the magnet core (2) at a constantspacing (15) parallel from the end face (12) of the magnet core (2). 23.The magnet valve of claim 21, wherein the damping face (20) extends inthe second end face (5) of the magnet core (2) at an angle (17) relativeto the end face (12) of the magnet armature (10).
 24. The magnet valveof claim 21, wherein the damping face (20), on the second face end (5)of the magnet core (2), has a luglike protrusion (32) that defines thehydraulic damping chamber (31).
 25. The magnet valve of claim 18,wherein the non-magnetic material (16) is a plastic material.
 26. Themagnet valve of claim 21, wherein the non-magnetic material (16) is aplastic material.
 27. The magnet valve of claim 18, wherein thenon-magnetic material (16) is glued to the second end face (5) of themagnet core (2).
 28. The magnet valve of claim 21, wherein thenon-magnetic material (16) is glued to the second end face (5) of themagnet core (2).
 29. The magnet valve of claim 26, wherein thenon-magnetic material (16) is glued to the second end face (5) of themagnet core (2).
 30. The magnet valve of claim 18, wherein thenon-magnetic material (16) is cast on the second end face (5) of themagnet core (2).
 31. The magnet valve of claim 19, wherein the dampingface (20) has a first annular face portion (21) in the radial direction.32. The magnet valve of claim 19, wherein the damping face (20) has asecond annular face portion (22) in the radial direction, below themagnet coil (3) that is let into the magnet core (2).
 33. The magnetvalve of claim 31, wherein the damping face (20) has a second annularface portion (22) in the radial direction, below the magnet coil (3)that is let into the magnet core (2), and wherein between the firstannular face portion (21) and the second annular face portion (22), agraduation (29, 30) is formed.
 34. The magnet valve of claim 24, whereinthe luglike protrusion (32) is embodied on a third annular face portion(23) of the damping face (20).
 35. The magnet valve of claim 18, whereinthe damping face (20) extends on the second end face (5) of the magnetcore (2) inside a remanent air gap (13) of the magnet valve (1).
 36. Themagnet valve of claim 23, wherein the damping face (20) is embodied inthe second end face (5) of the magnet core (2) in inclined fashionrelative to the end face (12) of the magnet armature (10) by an angle(17) such that the hydraulic damping chamber (31) opens in the radialdirection.
 37. The magnet valve of claim 23, wherein the damping face(20) is oriented on the second face end (5) of the magnet core (2)relative to the end face (12) of the magnet armature (10) at an angle(17) such that the cross section of the hydraulic damping chamber (31)narrows continuously in the radial direction.